The present invention is directed to a perfluorochemical emulsion which is useful as an artificial blood for the transport of oxygen.
Natural whole blood is in short supply, and the shortage will probably increase. New methods for prolonged preservation of blood in the frozen state and improvements in storage in the liquid state have resulted in more efficient use of available blood in some areas, but the world-wide need for blood for transfusion still far exceeds the supply. Since it is unlikely that there will be any appreciable increase in supply, needs must be satisfied by substances other than natural blood or its derivatives. An artificial blood, available in unlimited quantities and free from infectious agents and antigens, would be an extremely valuable therapeutic agent.
Emulsions of perfluoro compounds now seem likely to be successful as artificial blood. Perfluorochemical emulsion artificial bloods are free of infectious agents and antigens. (Hereinafter, perfluoro compound and perfluorochemical shall be used interchangeably.) Blood typing of the recipient is unnecessary. However, such artificial bloods lack clotting factors, platelets, immunoglobulins, and antibodies.
Perfluorochemical emulsions have been used successfully as substitutes for red blood cells in perfusing isolated animal organs and in the delivery of oxygen to the tissues of intact animals. Recently, an emulsion of perfluorochemicals was used in treating human subjects.
Although perfluoro compounds are chemically inert, they may adversely affect blood platelets and blood coagulation factors, resulting in thrombocytopenia (i.e., decrease in the absolute number of blood platelets) and disorders of blood coagulation. It has been found that the effects on platelets are likely due to unusual surface properties of perfluoro compounds, namely a very low surface tension. This effect can be overcome by coating the perfluoro compound particles with a substance which masks its surface activity.
The efficacy of perfluorochemical emulsions as artificial bloods is limited by the relatively short retention time of the emulsion particles in circulation. It would therefore be desirable to provide emulsion particles which have an extended duration in circulation and do not affect platelet aggregation or clotting factors.
Artificial blood compositions comprising perfluorochemicals in phospholipid emulsifiers are known in the art. However, such prior art emulsions contain substantially less perfluorochemical, and substantially less emulsifier, than the present invention. They are also substantially less stable.
U.S. Pat. No. 3,958,014 discloses the preparation of a perfluorocarbon emulsion in lecithin. The preferred concentrations of perfluorocarbon and lecithin are 25-30% (w/v) and 3-5% (w/v), respectively. (Hereinafter, "% (w/v)" shall mean the amount of a material, measured in grams, contained in 100 ml of emulsion; "% (v/v)" shall mean the volume of a material measured in ml, contained in 100 ml of emulsion.)
U.S. Pat. No. 3,962,439 teaches perfluorochemical emulsions in lecithin containing 10-40% (w/v) perfluorocarbon and 2-6% (w/v) lecithin. The emulsions of this patent are unstable.
"FLUOSOL-DC" is an emulsion prepared by Green Cross Corporation (see brochure dated May 15, 1975 "Technical Information Ser. No. 1", p. 38-39). "FLUOSOL-DC" must be stabilized by pasteurization at 60.degree. C. for one hour on three successive days since heat sterilization at 100.degree. C. destroys the emulsion. It must be sterilized under relatively mild conditions--repeated heating at 60.degree. C. Within six hours after infusion into the recipient, the phospholipid layer surrounding the perfluorcarbon particle decays. The nude perfluoro particles then disappear from the circulation.
U.S. Pat. No. 4,105,798 teaches a perfluorochemical emulsion in lecithin containing 10-30% (v/v) perfluorocarbon and 1-5% (v/v) lecithin.
It was recently discovered that an emulsion of improved stability results from the combination of two perfluorochemical compounds. The emulsion which is the subject of U.S. Pat. No. 4,252,827 is an emulsion of two perfluorocarbons (10-50% w/v total), in a high molecular weight nonionic surfactant emulsifier (2.0-5.0% w/v), a phospholipid "emulsifier adjuvant" (0.1-1.0% w/v), and a fatty acid (0.004-0.1% w/v). This composition, although more stable than other compositions, is of limited utility. It is prepared and stored in three separate components which must be kept frozen until just prior to the time of infusion. Infusion must occur within 24 hours of thawing and mixing. Thawing results in loss of emulsion stability. Most significantly, this emulsion cannot be autoclaved by conventional techniques. Sterilization is carried out at 115.degree. C. for 12 minutes in a specially designed rotary sterilizer. Emulsions of U.S. Pat. No. 4,252,827 are isotonic, but hyperionic.
"PLURONIC F-68", a high molecular weight nonionic surfactant, is the emulsifier used in "FLUOSOL-DA", a composition prepared according to U.S. Pat. No. 4,252,827 which is a product of Green Cross Corporation of Japan. Investigators have found that "PLURONIC F-68" inhibits blood coagulation and aggregation of platelets.